The present invention relates to a hydraulically operated mine roof support for use in underground excavations and comprising a support member adapted to rest on the floor of the underground excavation or mine gallery, a first shield fixed to and projecting upwardly from the rear end of the support member, a second shield pivotally attached to the upper end of the first shield and inclined with respect to the latter toward the mine face, a cap adapted to engage with its top face the roof of the mine gallery and being pivotally attached intermediate its ends to the upper end of the second shield so as to form a wedge shaped free space between the portion of the bottom face of the cap located rearwardly of the point of its attachment to the second shield and the upper surface of the latter, and an expandable and contractable prop between the support member and the second shield for changing the inclination of the latter and for pressing the top face of the cap against the roof of the mine gallery.
In mine roof supports of the aforementioned kind there is always the danger that the aforementioned wedge-shaped space becomes filled with loose rock material so that, especially when the prop is partially contracted during movement of the roof support from a portion of the mine gallery of greater height to a portion of smaller height, the front end of the cap directed toward the mine face cannot be brought into engagement with the mine roof. In this case a portion of the mine roof above the front end of the cap will not be properly supported so that loose rocks may fall down from the unsupported portion of the mine roof which will lead to a dangerous situation and to undesirable mixing of such rocks with the coal to be mined.
A mine roof support is already known from the German Gebrauchsmuster 7,304,941 in which the cap is constructed in a special manner in an attempt to overcome this problem. In this known construction the cap is provided with side walls which taper toward the front end of the cap and the upper end portion of the second shield, which is reduced in width, is pivotally connected to the cap intermediate the ends of the latter and arranged to be located in certain angular positions of the second shield and the cap with respect to each other at least in part in a cut-out provided in the top wall of the cap. This known construction results in a weakened cap and will not positively prevent loose rocks from penetrating into the mentioned space.